<!DOCTYPE html>
<html lang="en">
    <!-- 作用在子元素上 -->
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .son:nth-child(1) {
  background-color: olivedrab;
  flex-grow: 0;
}
.son:nth-child(2) {
  background-color: red;
  flex-grow: 1;
}
.son:nth-child(3) {
  flex-grow: 10;
  background-color: orange;
  margin-bottom: 0px;
  margin-right: 0px;
}
    </style>
</head>
<body>
    
    <div>
      <div class="son">son1</div>
      <div class="son">son2</div>
        <div     class="son">son3</div>
    </div>
</body>
</html>